A kit is provided for making a panel structure (3) for an external side wall or a covering of a building (1); the kit has a plurality of section elements (6) elongated along a longitudinal axis (7), designed to be fastened to a support (2) and having respective seats (14) which are open at the top and at their longitudinal ends and are designed to form, together, a longitudinal channel (15); the kit is provided with panels (21), engaging the channel (15), and with a seal (24) made of flexible material and having a strip portion (25) to cover at least two consecutive joint zones between the section elements (6).